NFPA 70E HRC Hazard Risk Category Levels explained

In it’s most basic form HRC level 1 is low risk and HRC 4 is the most dangerous.

HRC level is determined by the minimum amount of calories per square centimeter (ATPV or Cal/cm2) a treated garment must pass through with a 50% probability of a 2nd or 3rd degree burn occurring, thus the protective level of the treated clothing. The higher the ATPV, the higher the HRC level attained, the greater the protection.

The following HRC level chart / table /matrix shows minimum ATPV value that must be calculated to acquire the next level of HRC and typical FR apparel used to accomplish the ATPV/HRC calculation.

NOTE: Layering is generally gives more protection than the sum total of the ATPV values of the individual garments being layered. However, this needs tested for each specific garment being layered and thus is never explicitly included in layered calculations, but rest assured layering FR clothing grants you at least some extra protection.

What is NFPA 70E?

The National Fire Protection Agency (NFPA) created NFPA 70E, a Standard for Electrical Safety in the Workplace. NFPA 70E standard was the first nationally recognized standard for electrical safety in the United States, and was the reference document used for the Electrical Safety-Related Work Practices (ESRWP) regulation (OSHA 29 CFR 1910.331 through .335). The first edition was released in 1976 at the request of OSHA to help provide consensus on electrical safety standards. As of 2007 it has been revised seven times with new editions expected in 2008 and 2009.

An arc flash (or arc blast) event is a type of electrical explosion that results from a low impedance connection to ground or another voltage phase also called a “short” in an electrical system. A short circuit can occur anywhere in an electrical system, usually during maintenance work when the unexpected occurs. For instance a tool dropping, a wire slipping out of your hand a mechanical accessory falling loose and so on. A dangerous arc flash can only occur if the fault current is very high – in the range 1000 amps or more. The massive energy released in the fault instantly vaporizes the metal conductors involved, blasting molten metal and expanding plasma outward with extreme force. A typical arc flash incident can be inconsequential but could conceivably easily produce a more severe explosion. The result of the violent event can cause destruction of equipment involved, fire, and injury not only to the worker but also to nearby people. [thermal,fire] – [wikipedia ]

Arc Rating

A value of the energy necessary to pass through any given fabric to cause with 50% probability a second or third degree burn. This value is measured in calories/cm2. The necessary Arc Rating for an article of clothing is determined by a Hazard/Risk Assessment and the resulting HRC. Usually measured in terms of ATPV or EBT. [standards]

ATPV (Arc Thermal Performance Value)

A reported value from electric arc testing. Basically, it is the measure of how much heat can be exposed to a flame resistant garment before a second degree burn injury is expected to occur. [abbreviation,thermal,fire]

Calorie

The energy required to raise one gram of water one degree Celsius at one atmosphere pressure. Second-degree burns occur at 1.2 calories per centimeter squared per second (cal/cm2). [energy]

A Cigarette lighter placed under your finger for 1 second equals roughly a 1 calorie burn.

A 100 cal/cm2 blast can reach temperatures of up to 35,000 degrees Fahrenheit in the center, and 11,000 degrees on the perimeter

Electric Arc

The passage of substantial electric current through ionized air. [thermal,fire] (see ARCFLASH)

Electricity

the flow of an atoms electrons through a conductor. [energy,electrical]

Electronically Safe Work Condition

When the conductor or circuit part to be worked on has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary. [energy,electrical]

Flame resistant

The characteristic of a fabric to resist ignition and to self extinguish if ignited. [thermal,fire]

Abbreviated as FR.

Flame retardant

A chemical substance used to impart flame resistance – not part of the basic fibers chemistry. Flame retardant treatments can diminish overtime or with use. [thermal,fire]

Flammability (Vertical Flame Test)

Measures char damage length, afterflame and afterglow time on a 3″ × 12″ fabric sample exposed to flame at its lower edge for 12 seconds. (Contact us to get a free burn-swatch of Benchmark FR ring-spun cotton to perform your own test!). [thermal,fire]

A dangerous condition caused by the release of energy from an electric arc. [electrical,fire,thermal]

Flash Hazard Analysis

A study investigating the potential exposure to arc-flash energy that a worker faces while performing a specific job task. The data collected in a Flash Hazard Analysis is used for the purpose of injury prevention and the determination of safe work practices and the appropriated levels of FR clothing and PPE.. [fire,standards]

Flash Protection Boundary

The distance from an exposed live part within which a person could receive a second-degree burn if an electrical arc were to occur. [fire,standards]

FR

See flame resistant. [abbreviation]

HRC (Hazard Risk Category)

The classification of the listed task according to the type of hazard present when performing the task. Zero represents minimal risk, four represents the greatest risk. [abbreviation,standards]

The five Hazard/Risk categories are specified by the chart listed in NFPA 70E. The chart, based on specific job tasks, ranges from HRC 0 (which is low risk and allows for 100% untreated cotton), up to HRC 4 (which is high risk and requires FR clothing with a minimum arc rating of 40). The HRC is used to determine the necessary arc rating of a garment worn during a given job task. [standards]

The standard contains definitive criteria for establishing an effective program for locking out or tagging out energy isolating devices and requires training for authorized and affected employees. [abbreviation,electricity,standards]

NFPA writes voluntary compliance standards related to the Fire Service and other industries. Also works directly with OSHA for establishing legal regulations for electrical safety (see NFPA 70E). [abbreviation,standards]

OSHA bases its electrical safety mandates on NFPA 70E®: Standard for Electrical Safety in the Workplace®. OSHA evaluates compliance with its electrical safety regulations, OSHA 1910 Subpart S and OSHA 1926 Subpart K, using the comprehensive information in NFPA 70E. While OSHA tells you what to do to avoid electrical dangers, this vital Standard tells you how. [standards]

The resistance to flame and associated thermal transfer through the garment. [thermal,fire]

TPP (Thermal Protective Performance)

A fabric specimen is exposed with a combination of radiant and convective energy. The total energy required to cause second-degree burn injury to human tissue is determined based on heat transfer through the fabric specimen and the Stoll second-degree burn criteria. Single and multiple layer fabric specimens can be tested. [thermal,fire]

Hazard Risk Assessment

By OSHA standards it is up to your employer to conduct a Hazard Risk Assessment and determine the required level of protection for the tasks you will be required to perform. However, we recommend that you are aware of the information that NFPA 70E attempts to protect you from and what HRC means so that you can be confident that you are adequately protected.

When conducting a Hazard Risk Assessment the electrical equipment being tested is assessed for the the potential of an explosion or ARC flash, which is also measured in Cal/cm2. Simply stated, the goal is to always have more protection than the potential energy that could be output during an explosion or ARC flash.

ARC flash information

Benchmark FR ATPVHRC layering calculatorTry layering different Benchmark FR apparel and even non-FR clothing to achieve the desired HRC level. Humorous but serious tool will teach a few things and make you laugh.